1. Field of the Invention
The present invention relates to a surface profile measuring machine equipped with a contact-type detector with a stylus and an image probe and to an offset amount calibrating method for obtaining the offset amount between the contact-type detector and the image probe.
2. Description of Related Art
There has been known a surface profile measuring machine in which a stylus is moved along a surface of an object while being in contact with the surface of the object. The displacement of the stylus due to the surface profile or surface roughness of the object is detected, thereby measuring the surface profile, surface roughness and the like of the object based on the displacement of the stylus (see, for instance, Patent Literature: JP-A-05-087562).
In such a typical surface profile measuring machine, in order to measure the surface profile, surface roughness and the like of an object, while visually checking and adjusting the relative position between the tip end of a stylus and a measurement area on the object, an operator sets the tip end of the stylus at a measurement starting position on the object and then moves the stylus along the surface of the object. The surface texture such as the surface profile and the surface roughness of the object is measured based on the up-and-down movement of the stylus due to the surface profile, surface roughness and the like of the object.
Due to a recent tendency for measuring minute and thin objects, objects or measuring spots are downsized. Accordingly, the above setting operation of a stylus, which is quite complicated and requires a long time, places a large burden on an operator.
In addition, some types of objects may interfere with (collide with) a stylus to damage the stylus or the objects.
Accordingly, the Applicant(s) has worked on the development of a surface profile measuring machine equipped with not only a contact-type detector with a stylus for contacting with a surface of an object but also an image probe used to capture an image of the surface of the object.
In such a machine, the image of the object is initially taken by the image probe. When a measurement starting position on the object is designated based on the taken image of the object, the movement course of a relative movement mechanism is calculated and stored so that the stylus of the contact-type detector is in contact with the measurement starting position on the object. In response to a command for measurement, the relative movement mechanism is moved in accordance with the stored movement course, so that the stylus of the contact-type detector is automatically brought into contact with the measurement starting position on the object.
In this manner, the stylus of the contact-type detector can be automatically set at the measurement starting position on the object. In other words, an operator does not have to set the tip end of the stylus at the measurement starting position on the object while visibly checking and adjusting the position of the tip end of the stylus relative to the measurement starting position on the object as in a typical apparatus. Accordingly, the stylus can be prevented from interfering with the object while reducing the burden on the operator.
However, the contact-type detector with the stylus and the image probe are offset from each other in the same system for physical and structural reasons.
Therefore, at the time of switching from the image probe to the contact-type detector or switching from the contact-type detector to the image probe, the offset amount between the contact-type detector and the image probe has to be corrected. Thus, it is important for realizing highly-accurate measurement to accurately obtain the offset amount between the contact-type detector and the image probe.